A means has been widely used to vary the friction coefficient and contact pressure of a wheel by interposing an anti-skid deterrent between the wheel and the road surface. For this purpose various anti-skid deterrents and devices are known. For example, in order to prevent skidding on frozen roads, sand and caterpillar tread devices or caterpillars have been commonly used.
The drawback of sand strewn on frozen roads for skid prevention is that it can be used only in limited areas because of the amount needed and the cleanup required afterwards.
Caterpillars are used for military tanks, snow mobiles and construction machines. However, caterpillars are not only difficult to attach and remove; but are heavy themselves.
In order to overcome these drawbacks, studded tires or anti-skid chains have been used on frozen roads. However the present studs and chains are still difficult to attach and remove, through not as difficult as caterpillars. Consequently many drivers leave them on continuously even when they are unnecessary on normal roads. Therefore their use results in damaged roads, giving rise to wheel dust pollution and also damaging the studs or the chains. In addition, their use is accompanied by other problems like fuel waste and unpleasant driving.
In order to solve the above mentioned problems, various inventions have been devised to make it possible to interpose an anti-skid deterrent only when necessary. For example, in a specification of JP. A, 54-151202 (GORAN TORNEBACK) or British patent 110,674 (HAROLD THORNE), relevant devices are shown which use a bunch of short chains consecutively inserted under a tire or trodden as anti-skid deterrents. In these devices chains rotated about a center are imposed under a wheel by the centrifugal force due to the gyration of the chains. Therefore they can work when going up a slope or starting, and can be used only when necessary. However, one drawback is that the chains cannot be imposed under a wheel when braking because of the absence of gyration.
In order to solve this shortcoming, German patent--DE, B, 1162216 (HANNS SCHNITZLER) is known to work when braking. In this specification a treading device with elastic anti-skid blades are attached to a gyrating boss. When the gyration centers of the boss and the wheel are at the appropriate positions with respect to the advancing direction of the wheel, this circular motion device enables the treading or imposition of the elastic anti-skid blades under the wheels when accelerating as well as braking. Such skid prevention function can be enhanced when studs are attached to the anti-skid blade.
However, the devices based on the circular motion as shown in the above-mentioned specifications have three serious faults which are interrelated to one another. Therefore none of these means have proven to be practical. These faults are as follows;
A. Inability to continue a smooth treading of anti-skid blades. PA0 B. Inability to make both the anti-skid blades and the device strong and durable. PA0 C. Difficulty in reducing the size of the device.
The main reason is the locus difference on the road between the tread of the tire and the blade of the anti-skid device--the former along a linear line with no lateral component and the latter having a quasicycloid resultant between the gyration of the blade and the vehicle motion. The moving length of a blade under the tread is shorter than the length of the tread. Therefore the effects of the locus difference seem insignificant.
However, experiments have shown the enormous effects of the difference. In order to discuss the motion in detail, the tire tread on which the anti-skid blade moves can be divided into two parts--1) the half between the tread front and the center and 2) the half between the center and the tread tail. In the first half, the trodden part of the blade becomes wider toward the connected end with the blade rotating. In the second half, the blade begins to be subjected to tension, since the trodden position or portion of the blade under the tire tread recedes from the rotation center. The greater the lateral motion component of the blade motion in the short radius circle, the stronger the tension upon the blade. The trodden part of the blade caught or compressed between the tire tread and the road surface stays at a fixed position on the road, while the other end connected to the center boss advances. The anti-skid blades are subjected not only to the above-mentioned tension but to twisting. The combination of the tension and the twisting will make the blades vulnerable to stress damage. Besides, as the trodden blade rotates and passes by or through the tread tail, the blade is released suddenly from the previous tension. Consequently, the repetition of this action will cause vibration which could be the cause of malfunctions.
On the other hand, when the radius of the circular motion of the blades is increased in order to reduce the locus difference, the blades must be stiffer to facilitate continuous gyration. The enlarged size and the stiffer blade make buffering or shock absorption more difficult. Consequently obstacles on a road can more easily damage the enlarged device. So it has not been possible to make a practical model.
If the supporting structure or main holding mechanism is strengthened so as to avoid the difficulties due to vibration, the device becomes vulnerable to malfunction due to lack of any shock absorbing or buffering function.
Furthermore, another difficulty of the circular motion of the rotating device is that the holding arm is not always stable, since in such position the holding arm can be connected only to a portion of such device near the gyration center.
Furthermore, the rotating anti-skid blades of the prior art have another fault. It has been proved in experiments that they prevent smooth operation or running of wheels of the vehicle; since, consuming energy, the action that deforms, twists and damages by the anti-skid blades interferes with the smooth rotation of the wheels.
Another point is that, when studs are installed in a blade to increase the friction coefficient, they are jarred or jerked by the blade. Therefore one difficulty or fault is not only that the studs and the peripheries of studs in a blade are subjected to excessive damage, but that the lateral motion of the studs and the blades make the coefficient of friction a dynamic one which is less than a statical one.
The objective of the present invention is to provide a treading device for wheels which is light, small, and strong to obviate the above mentioned faults, and yet provide smooth driving.